Vacuum-tube system



March 4, 1930.

D. G. LITTLE VACUUM TUBE SYSTEM Filed Jan. 25, 1924 ATTORNEY 40 high resistance.

I 50 used they I were Patented Mar. 4, 1 930 UNITED STATES PATENT OFFICE Application filed January 25, 1924. SerialNo. 688,383.

My invention relates to radio frequency generating systems.

One object of my invention is to provide means for increasing the efiiciency of a gen- 5 erato'r for producing modulated, radio-frequency currents.

Another object of my invention isto provide means for use in connection with a ra- (ho-frequency oscillation generator and modulator apparatus which will increase the effi- 1 ciency of operation of both the generator and theimodulator in the production of modulated, radio-frequency oscillations.

Another object of my invention is to provide means for damping out the very high frequency parasitic oscillations in a triode which the'internal capacity of the triode tends to produce when combined with connected inductance and capacity'in exterior circuits,

without reducing the flow of normal frequency currents.

Inthe operation of high-power radio-frequencyv oscillation generators using a, plurality of triode thermionic discharge devices connected according to the Heising constantcurrent modulation system with thevery low impedance triodes and the high voltages which are essential for the conversion of a considerable quantity of power into the form 0 of modulated radio-frequency oscillatory energy, difficulty has been encountered in obtaining satisfactory efliciency and satisfactory purity of vibration frequency.

. In the prior art of the operation of'triode A devices, it has been found desirable for many purposestoinsert into the grid circuit of the devic'e various, impedances. In many instances, the impedance device inserted con 7 sisted in, part ofa condenserand inpart'of a This resistance served to maintain the average mean voltage difference between the grid and cathode at a value to cause the device to function in a predetermined way. In eachcase, the resistance was shunted by a condenser which passed alternating current freely. By this means, the grid was maintained at a desired potential without restraining the access of alternating current to it. When such resistances were customarily connected in shunt to some other impedance in the same circuit and ranged in value from 100,000 ohms to one or more megohms.

It has been found that a considerable amount of electrostatic capacity is present between the various connected circuits of such a triode operating system. This capacity, in conjunction with the capacity of the tube itself, and the inductance of the various circuit elements to which it is connected produce a condition which tends to cause each triode to oscillate independently at an extremely high parasitic frequency. This parasitic oscillation is objectionable because of the waste of power which it causes and because of the heating which it produces in the triode, and, also, because of the possibility of some of it being radiated by the same system which generates and radiates the signal wave and thereby producing an impure radiated wave.

The device of my invention is a means which substantially prevents these parasitic oscillations, both in oscillator triodes and in modulator triodes.

, Other objects and structural details of my invention will be apparent from the following description when read in connection with the accompanying drawings, wherein Figure l is a diagrammatic view of a radiosending apparatus comprising my invention,

and

Fig. 2 is a diagrammatic View of the elements of a triode and its connected circuits and the capacities and inductances in those circuits.

Referring to Fig. 1, a radio-sending aerial 1, a connected inductance 2 and a ground 3 comprise an elementary radiating system. To this system is connected a pair of oscillator triodes 4 and 5 having anodes, grids and cathodes. The drawing further shows another pair of triodes 6 and 7 connected as modulators, a direct-current source 8, an inductance 9, a modulation transformer 11 and a source of filament heating current 12. These various elements are connected, as indicated, by conductors as required for constant current modulation systems. In the grid leads of triodes 4, 5, 6 and Y are connected resistors capacity of the triode plays a triode.

14, 15, 16 and 17, which are the means that The capacity between leads 28 and 29 is indi cated as a condenser 32. The capacity between the grid 22 and the anode 23 is indicated as a condenser 33. In the circuit between the grid 22 and the inductance 27 is indicated; a resistor 34. Similar grid leads to'triodes 4, 5, 6 and 7 are indica-ted at 35,

and plate leads at 36. V e

The circuitsand apparatus shownin Fig. 2, comprising the triode 21 having a'low internal impedance,

which oscillations may be generated upon the application of sufliciently high voltage to the 25 serves as a plate The inductance inductance, the inductance 27 serves as a grid inductance, condensers 31 and 32 in series serve as a portion ofa circuit for high-frequency between the inductance 25 and 27, and

condenser 33 serves as a means for completing a circuit whereby energy is transferred from the inductance 25 to the grid 22. The capacity 33 cooperates with the inductance 27 to impress voltage changes upon grid 22in the proper phase displacement to cause the triode 21 to be set into a condition of oscillation at. a frequency determined by the values of inductance and capacity in the cirv cuits. y

In the system of Fig. 2, a resistance 34 is connected between the grid22 and the grid lead 28. This resistance, so connected, is in a position intermediate the capacity 33, which is the capacity of the triode 21 and inductance 27 of the grid conductor of the triode. This resistance 34 is a damping resistor which limits the current flow to grid 22. This limiting efiect damp s out undesired high-frequency oscillations because of the fact that the generation of such oscillations is possible only because of the flow of oscillatory energy through the capacity of tube-21.

- In the development of the normal desired oscillation frequency in a triode system, the

very sub-ordinate part in the necessary transfer of voltage to the grid to produce oscillation. Instead, V

the energy is furnished by coupling between the grid andplate coils. For this reason, a very limited amount of current flows to the grid for the production of the oscillations of the desired frequency. Because of this fact,

constitute a system in odes of a resistor in the jgridcircuit exercises a proportionately greater damping action on the undesired frequency than on the desired frequency, since the energy of the undesired frequency must all be transferred through the tube capacity and the grid lead while the desired energy is not so transferred. The ratio can be still further increased by increasing the effective voltage applied to the grid from the grid inductance by increasingthe connected turns of the grid coil. This increase of voltage compensates for the small amount of energy lostin the resistance. r

In the oscillator system represented 1n Fig. 1, which is designed for the generation of a customary radiofrequency, inductances 25 and 27 may be represented by straight conductors 35 and 36. It is not necessary for tance be in the form of actual coils. Under these conditions, the same straight conductor forms both a part of a'conden'ser and an inductance as well. This condition is present in the typical radio-frequency g i paratus, as will be evident from Fig. 1; I The resistors 14, 15, 16 and 17 in Fig. perform the function for their respective t'r1' odes 4, 5, 6 and 7 that is indicated as the function of resistance 34 of Fig. 2. The values of these resistors may bebetween and 50,000 ohms for most effectiveoperation. By this means, I am able to reduce to a negligible magnitude-the parasitic oscillations 10,000 ohms 5 r 'enerating ap- V Y 2 developed in the triodes of a modulator Sys- 7 1 ence with their operation for the generation of oscillations at a lower While I have shown only one embodiment of my invention in the accompanying drawings, it is capable of various changes and modifications without departing from the spirit thereof, and it is thereon as areindicated in the prior art or in the appended claims.

I claim as my invention:

1. Ina radio system, a plurality of modulator'tubes, a connection between the cathsaid tubes, a common connection between the anodes ofsaid tubes, a source of modulating potential, means for connecting the input circuits of said tubesin parallel to.

said source, and a plurality of high-resistance devices respectively individual to said'tubes and respectively connected between the grids thereof and their common connection to said source of modulating potential. V

2. In a wave transmission system, a plurality of oscillator tubes, a connection between the cathodes of saicl tubes, a common connection between the anodes of said tubes, an oscillatory circuit, means the input circuits ofsaid tubes in parallel to for connecting desired frequency. I j

desired, therefore, I, that only such limitations shall be imposed said oscillatory circuit and a plurality of high-resistance devices respectively individual to said tubes and respectively connected between the grids thereof and their common connection to said oscillatory circuit.

. b 3. In a wave transmission system, a plu-.

rality of modulator tubes, a plurality of oscillator tubes, a common connection between the anodes of all of said tubes, a common connection between the cathodes of all of said tubes, an oscillatory circuit, means for connecting the input circuits of said oscillator tubes in parallel to said oscillatory circuit, a source of modulating potential, means for connecting the input circuits of the modulator tubes inparallel to said source, and a plurality of high-resistance devices respectively individual to the input circuits of said tubes and respectively connected between the grids of the oscillator tubes and the oscillatory circuit and the grids of the modulator tubes and the source of modulating potential, whereby the generation of oscillations at parasitic frequencies is prevented. In testimony whereof, I have hereunto subscribed my name this 21st day of January,

, V DONALD G. LITTLE. 

